PIC18F2450/4450
A fixed delay of interval TCSD, following the wake event,
is required when leaving Sleep and Idle modes. This
delay is required for the CPU to prepare for execution.
Instruction execution resumes on the first clock cycle
following this delay.
3.4.3
RC_IDLE MODE
In RC_IDLE mode, the CPU is disabled but the periph-
erals continue to be clocked from the internal oscillator,
INTRC. This mode allows for controllable power
conservation during Idle periods.
From RC_RUN, this mode is entered by setting the
IDLEN bit and executing a SLEEP instruction. If the
device is in another Run mode, first set IDLEN, then set
the SCS1 bit and execute SLEEP. Although its value is
ignored, it is recommended that SCS0 also be cleared;
this is to maintain software compatibility with future
devices. When the clock source is switched to the
INTRC, the primary oscillator is shut down and the
OSTS bit is cleared.
3.5.2
EXIT BY WDT TIME-OUT
A WDT time-out will cause different actions depending
on which power-managed mode the device is in when
the time-out occurs.
If the device is not executing code (all Idle modes and
Sleep mode), the time-out will result in an exit from the
power-managed mode (see Section 3.2 “Run
Modes” and Section 3.3 “Sleep Mode”). If the device
is executing code (all Run modes), the time-out will
result in a WDT Reset (see Section 18.2 “Watchdog
Timer (WDT)”).
When a wake event occurs, the peripherals continue to
be clocked from the INTRC. After a delay of TCSD fol-
lowing the wake event, the CPU begins executing code
being clocked by the INTRC. The IDLEN and SCS bits
are not affected by the wake-up. The INTRC source will
continue to run if either the WDT or the Fail-Safe Clock
Monitor is enabled.
3.5.3
EXIT BY RESET
Normally, the device is held in Reset by the Oscillator
Start-up Timer (OST) until the primary clock becomes
ready. At that time, the OSTS bit is set and the device
begins executing code.
3.5
Exiting Idle and Sleep Modes
The exit delay time from Reset to the start of code
execution depends on both the clock sources before
and after the wake-up and the type of oscillator if the
new clock source is the primary clock. Exit delays are
summarized in Table 3-2.
An exit from Sleep mode or any of the Idle modes is
triggered by an interrupt, a Reset or a WDT time-out.
This section discusses the triggers that cause exits
from power-managed modes. The clocking subsystem
actions are discussed in each of the power-managed
modes (see Section 3.2 “Run Modes”, Section 3.3
“Sleep Mode” and Section 3.4 “Idle Modes”).
Code execution can begin before the primary clock
becomes ready. If either the Two-Speed Start-up (see
Section 18.3 “Two-Speed Start-up”) or Fail-Safe
Clock Monitor (see Section 18.4 “Fail-Safe Clock
Monitor”) is enabled, the device may begin execution
as soon as the Reset source has cleared. Execution is
clocked by the INTRC driven by the internal oscillator.
Execution is clocked by the internal oscillator until
either the primary clock becomes ready or a power-
managed mode is entered before the primary clock
becomes ready; the primary clock is then shut down.
3.5.1
EXIT BY INTERRUPT
Any of the available interrupt sources can cause the
device to exit from an Idle mode, or the Sleep mode, to
a Run mode. To enable this functionality, an interrupt
source must be enabled by setting its enable bit in one
of the INTCON or PIE registers. The exit sequence is
initiated when the corresponding interrupt flag bit is set.
On all exits from Idle or Sleep modes by interrupt, code
execution branches to the interrupt vector if the GIE/
GIEH bit (INTCON<7>) is set. Otherwise, code execution
continues or resumes without branching (see
Section 8.0 “Interrupts”).
© 2006 Microchip Technology Inc.
Advance Information
DS39760A-page 39
MICROCHIP [ MICROCHIP ]
